Multi-loop antenna and superregenerative detector



Dec. 16, 1969 I. J. ABEND 3,434,697

I MULTI-LOOP ANTENNA AND SUPERREGENERATIVE DETECTOR Filed Aug. 27, 19652 Sheets-Sheet 1 JV/4'6 c]. 46600 WWW Dec. 16, 1969 l. J. ABEND3,434,697

MULTI 'LOOP ANTENNA AND SUPERREGENERATIVE DETECTOR Filed Aug. 27, 1965 2Sheets-Sheet 2 1N VEN TOR MV/NG (1. 48600 United States Patent 3,484,697MULTI-LOOP ANTENNA AND SUPER- REGENERATIVE DETECTOR Irving Ll. Abend,Bergenfieltl, N.J., assignor to Lear Siegler, Inc., Santa Monica,Calif., a corporation of Delaware Filed Aug. 27, 1965, Ser. No. 483,186Int. Cl. H01q 19/00; H04b 1/22 U.S. Cl. 325-373 15 Claims ABSTRACT OFTHE DISCLOSURE This invention relates to radio receiving systems andmore particularly it concerns a novel antenna and input circuitarrangement for use in connection with receivers of the portable type.

The present invention finds particular utility in connection withelectronic paging systems wherein coded signals are sent out from acentral station and are monitored by portable receivers carried byvarious personnel. When a particular receivers code is transmitted onlythat receiver will respond to indicate that it has been called. Theperson being called then knows he should report back to the centralstation.

The individual receivers used in such electronic paging systems must, ofcourse, be very compact. They must possess a high degree of sensitivityand yet they must remain stable under conditions of temperaturevariation and other ambient changes. Also, since a great number ofpersonnel may be included in a given system, it is important that theconstruction of these receivers be maintained as simple and asinexpensive as possible.

One particularly critical area in the make up of a receiver of thisnature is the antenna. In order to capture incoming signals with areasonable degree of sensitivity and selectivity, it is important thatthe antenna have a high area-turns characteristic. The available areahowever, is limited by the physical confines of the receiver itself. Onthe other hand, the number of turns in the antenna coil is limited bythe fact that a large number of turns reduces the size of the associatedcapacitor to a point where the distributed capacitance of the antennacoil may have a significant, and to a great extent, uncontrolled elfect.In prior systems which used antenna coils of wire wound about a form,variations in the electrical characteristics of the antenna would occurwith changes in temperature as a result of the changes in stressproduced on the various turns of the coil due to expansion andcontraction. Furthermore, since the wire in the antenna coil was not ofuniform cross section and was not wound with absolute uniformity, thechanges in antenna characteristic which occurred over a temperaturecycle were not predictable and would vary from cycle to cycle.

It is also important that the antenna be made as insensitive as possibleto the effects of nearby magnetic materials; and this should beaccomplished with as little loss of antenna Q, or sensitivity, aspossible. Prior antenna coils were wound about the receiving system withthe various metallic components of the system being located 3,484,697Patented Dec. 16, 1969 directly within the core region of the coils.This of course greatly influenced and destabilized the antenna.

Another critical area in a paging receivers design lies in the circuitarrangement which receives signals from the antenna. This circuitarrangement must be capable of selecting the received signal and ofextracting from it the modulation or informational content which wasimposed at the transmitter station. Of the various arrangementsavailable in this connection, the superregenerative circuit is mostadvantageous. This circuit, which sequentially goes into and out ofcarrier frequency oscillation at an ultra-sonic rate, provides very goodsignal selectivity and sensitivity with a minimum of components. Thereare however certain difficulties associated with the use ofsuperregenerative circuits. For example, these circuits in priorarrangements were very sensitive to variations in componentcharacteristics due to temperature effects and aging. They were alsoquite sensitive to changes in the associated power supply voltage.

The above and other ditficulties are eliminated by the presentinvention. According to this invention there is provided a radioreceiver input arrangement characterized by a high degree of stabilityand frequency control without any increase in overall size orcomplexity.

In one aspect the present invention makes use of an antennaconfiguration comprising several physically displaced but electricallyconnected loops. As illustratively embodied these loops are formed on aprinted circuit board and are displaced near its outer periphery tomaintain a large area for efiicient utilization of the incident radiofrequency energy. Different portions of each loop are formed ondifferent sides of the printed circuit board and are connected byeyelets or plated conductive connectors. Individually adjustable coresof magnetic material are provided in each loop for flexibility of tuningand maintenance of a high Q factor. There is thus provided a multipleturn antenna coil of large area. The various turns of the coil moreoverare individually adjustable for very accurate tuning control. Also,these magnetic core elements serve to confine the magnetic fields oftheir respective loops, into the region immediately adjacent the loop.This effectively restricts the magnetic fields and keeps them away fromthe nearby electrical components and other metallic materials so thatthey Will not affect the antenna characteristics. Because the coil isprinted on a circuit board, there is provided an exceptionally highdegree of temperature stability. The individual loops are not subject tomechanical stress and the changes which they do experience withtemperature variations besides being minimal are also accuratelypredictable from temperature cycle to temperature cycle and from unit tounit.

In another aspect, the present invention provides a superregenerativecircuit configuration using a transistor having an antenna loop tankcircuit forming a feedback between its base and collector and aconnection through the resistance portion of a base-coupledresistance-capacitance quench circuit to a battery which is alsoconnected through a portion of the antenna coil to the collector elementof the transistor. This arrangement renders the circuit less sensitiveto variations in transistor characteristics due to temperature changesand aging; and it provides automatic compensation for variations in thevoltage source.

There has thus been outlined rather broadly the more important featuresof the invention in order that the detailed description thereof thatfollows may be better understood, and in order that the presentcontribution to the art may be better appreciated. There are, of course,additional features of the invention that will be described hereinafterand which will form the subject of the claims appended hereto. Thoseskilled in the art will appreciate that the conception upon which thisdisclosure is based may readily be utilized as a basis for the designingof other structures for carrying out the several purposes of theinvention. It is important, therefore, that the claims be regarded asincluding such equivalent constructions as do not depart from the spiritand scope of the invention.

A specific embodiment of the invention has been chosen for purposes ofillustration and description, and is shown in the accompanying drawings,forming a part of the specification, wherein:

FIG. 1 is a perspective view and partial schematic of a receiver inputarrangement according to the present invention;

FIG. 2 is an enlarged fragmentary section view taken along lines 2-2 ofFIG. 1; and

FIG. 3 is a composite diagram illustrating opposite sides respectivelyof a printed circuit board incorporating the present invention, saidsides being rotated out into a common plane about an imaginary axis X-X.

In the arrangement shown in FIG. 1, there is provided a fiat base boardof the type used for printed circuits. The board 10 is formed with aplurality of holes 12 distributed about generally toward its periphery.Tubes 14a of plastic or similar material extend through the holes 12 andprotrude out from the top of the board 10. These tubes are internallythreaded, as shown in FIG. 2, to accommodate adjustable cores 16 ofsolid magnetic material such as powdered iron. The cores 16 areexternally threaded for an adjustable but tight fit in the tubes 14; andthey are provided with hexagonal openings 18 in their ends so that theycan be turned with an Allen wrench.

As shown in FIG. 3, the board 10 is plated with conductive metal on bothsides thereof to form printed circuits 20. These circuits which may beformed according to known printed circuit techniques, are speciallyarranged, as indicated in FIG. 3, to provide proper interconnections andmountings for the various circuit components illustrated schematicallyin FIG. 1.

The printed circuits also form the basic portion of the novel antennaconfiguration of the present invention. As shown in FIGS. 1 and 3, theantenna, indicated generally at 21, begins at a first terminal 22 towardone edge of the board. It proceeds as a strip 24 of plated metal fromthis first terminal along the top of the board 10 to partially encirclethe first tube 14a. The strip 24 terminates at a first eyelet 26 whichas shown in FIG. 2, extends 4 through the board 10 to a correspondingpoint on its opposite side. A second strip 28 of plated metal continuesto encircle the tube 14a on the bottom of the board to complete a firstloop. The second strip 28 then proceeds along the bottom of the board tothe second tube 14b, which it also partially encircles. The second strip28 then terminates at a second eyelet 30 which extends up to the top ofthe board 10. A third strip 32 proceeds from the eyelet 30 around thetube 14b on the top of the board to complete a second loop and proceedsto the third tube 140. The looping process involving partialencirclement on both sides of the board 10 is repeated for each of theremaining tubes 14d to 14;. Upon proceeding from the last tube 14 thelast conductive strip terminates at a second terminal 33 whereconnections are made to the remaining portions of the circuit.

The particular manner in which the remainder of the superregenerativeinput circuit is attached to the board is not part of the presentinvention and thus it will be described in conjunction with theschematic diagram of FIG. 1.

As shown in FIG. 1, the six loop coils formed by the above describedantenna configuration are connected in parallel with a pair ofcapacitors 34 and 36 to form a resonant tank circuit. The firstcapacitor 34 is fixed and does not vary with temperature changes. Theother capacitor 36 however is designed to provide a negative temperaturecharacteristic which compensates for the temperature produced variationsin the inductance of the antenna coils. This tank circuitis connectedvia a line 38 to the collector terminal of the transistor 40. Theemitter of the transistor 40 is'coupled back via a capacitor 42to itscollector thus forming a feedback path. This feedback path is connectedto ground through a coil 44 which provides a DO path while preventingthe short circuiting of the radio frequency signals. A further capacitor46 is connected between the feedback capacitor 42 and ground to providean efiective radio frequency voltage divider arrangement in the feedbacknetwork so that the transistor 40 will not be driven too hard by the fedback signals.

A tap 48 is taken beyond one of the antenna loops and is connected via aresistor 50 to the base terminal of the transistor 40. The base terminalis also coupled to ground through a capacitor 52.

Power is supplied from a battery or other D.C. voltage source (notshown) through a pair of input'terminals 54, connected respectivelybetween ground and to a variable resistor 56. The tapped resistor 56 isconnected through a further resistor 58 to a point 60 between the tap 48from the antenna and the resistor 50 leading to the transistor baseterminal. A further capacitor 62 is connected between the point 60 andground; and demodulated output signals are taken from the point 60.

The values of the various resistors, inductors and capacitors in thesystem are chosen such that during normal operation, the oscillatorcircuit formed by the transistor 40, and the feedback capacitor 42 tendsto produce continuous oscillations at the particular radio frequency towhich the system is tuned. However, because of the manner in which theresistor 50 and capacitor 52 are connected between the power supplyinput terminals 54 and the base of the transistor 40, there is produceda variation in the base bias of the transistor 40, causing it toperiodically interrupt these oscillations. The rate at which thisquenching or interruption of oscillation takes place depends upon the RCtime constant of the capacitor 52 and the resistor 50; and, this ispreferably chosen to be within or beyond the audible range, and, ofcourse, beyond the modulation frequency used with the system.

While the circuit alternates between radio frequency oscillation and nooscillation at the quench frequency rate, modulated radio signals from aremote transmitter are received at the antenna 21 and these signalscause the resonant circuit formed by the antenna and the capacitors 34and 36 to resonate. The modulation appearing on the incoming signalproduces a variation in the average collecfor current of the transistorand this change in average current represents the actual modulation orinformation carried on the incoming signal.

The collector current also passes through the junction point 60. Thevariations in current at this point include the frequency of selfoscillation of the transistor arrangement the quench frequency and themodulation frequency. A low pass filter (not shown), such as a pi-typefilter, elfectively eliminates all but the modulation frequency which ispassed and amplified for use in the receiver system.

The transistor 40 serves as a very effective amplifier immediately priorto the onset of oscillation. However, because of circuit instabilities,it is difiicult if not impossible to keep it in this condition.Accordingly, the present system by means of the RC circuit 50, 52,successively biases the transistor above and below the point of selfoscillation so that the average overall gain is kept at a high value.

The above described arrangement is particularly suitable for use withminiaturized receiving systems. The antenna 21 is of multiloop designand encompasses a large area. It thus provides maximum efiiciency inabsorbing incident radio frequency energy so that maximum sensitivity isattained. Further, since the core configuration, comprising the magneticcores 16, is distributed, the sharpness of tuning or Q of the inputcircuit is maintainedat a high value. Of course, this also results in aminimization of losses.

Another, and very important feature associated with this antennaconfiguration is that the inductance changes produced by temperaturevariations are made uniform and predictable, these changes being verysmall in comparison to inductances wound in the usual manner withordinary wire. Further, the changes which do take place follow the samepattern from unit'to unit and over each temperature cycle.

By providing the one loop tap 48 in the antenna, it is possible toeliminate the capacity changes normal to the various components in thetank circuit including the transistor itself. Also, this arrangementreduces all other capacity efiects by the square of the tap ratio.

The several iron cores 16 serve to confine the magnetic fields in theregion to the individual loops, thus effectively isolating the antennafrom the effects of the other components on the same circuit board.Further, these coils, being individually tuneable to permit variation ofthe inductance ratio on either side of the tap 48. This provides aconvenient way to compensate for component variation and to tune thetank circuit thus allowing optimized performance of the receiver.

It will further be appreciated that the arrangement of the resistor andthe first loop to the antenna 21 between the collector and baseterminals of the transistor 40 serves to stabilize the action of thetransistor. Further, by using this loop as the power input point, it ispossible to stabilize the system from changes in the power supplyoutput.

Having thus described my invention with particular reference to thepreferred form thereof, it will be obvious to those skilled in the artto which the invention pertains, after understanding my invention, thatvarious changes and modifications may be made therein without departingfrom the spirit and scope of my invention, as defined by the claimsappended thereto.

What is claimed as new and desired to be secured by Letters Patent is:

1. A multi-loop antenna system comprising a flat, nonconductive basemember, a printed circuit arrangement on both sides of said base member,said printed circuit arrangement being configured to form portions ofelectrically connected but physically displaced and non-overlappingantenna loops on one side of said member and continuations of said loopson the opposite side of said member, said portions being electricallyconnected to their respective continuations through connector meansextending through said base member.

2. An antenna system comprising a generally fiat, nonconductive basemember having a plurality of holes formed therethrough, a printedcircuit arrangement on both sides of said base member, said printedcircuit arrangement being configured to form portions of loops aboutsaid holes on one side of said member and continuations of said loops onthe opposite side of said base member, said portions being electricallyconnected to their respective continuations through connector meansextending through said base member and individual core elements movablethrough said holes.

3. A multi-loop antenna system comprising a gener ally fiat,non-conductive base member, a plurality of conductors arranged onopposite sides of said base member, the conductors on one sideconfigured to form portions of electrically connected but physicallydisplaced and nonoverlapping antenna loops and the conductors on theopposite side being configured to form continuations of said loops, saidportions being electrically connected to their respective continuationsthrough connector means extending through said base member.

4. An antenna system as in claim 3 wherein said loops are laterallydisplaced from each other about said base member.

5. In combination with a radio receiving system, an

antenna arrangement comprising a plurality of conductive loopsphysically displaced from each other and connected in series to form anoverall loop and means mounting said conductive loops in displaced arraysuch that said overall loop surrounds the components of said receivingsystem.

6. A combination as in claim 5 further including individual cores ofmagnetic material positioned within said conductive loops.

7. A combination as in claim 6 wherein said individual cores areindividually adjustable into and out from their respective loops.

8. In combination a generally flat electrically nonconductive basemember, said base member being provided with printed wiring on bothsides thereof, a radio receiving circuit including electrical componentsmounted on said base member and connected through said printed wiring,an antenna forming a portion of said radio receiving circuit and mountedon said base member, said antenna comprising a plurality of individualloops distributed about said base member and connected together inseries to form a major loop which encloses said electrical components.

9. A combination as in claim 8 wherein said individual loops constitutea portion of said printed wiring on said base member.

10. A combination as in claim 9 wherein portions of said individualloops are formed on one side of said base member and continuations ofsaid individual loops are formed on the opposite side of said basemember, each continuation being electrically connected to itscorresponding portion through said base member.

11. An antenna system comprising a generally flat electricallynon-conductive base member formed with holes therethrough, individualinternally threaded tubular elements extending through said holes, aplurality of externally threaded cylindrical core members threadedlyengaged in said tubular elements, a plurality of electrically conductiveloops extending about said tubular elements and means connecting saidloops to each other.

12. An antenna system as in claim 11 wherein said core member are ofmagnetic material.

13. An antenna system as in claim 11 wherein a portion of each loop ison one side of said base member and the remainder of each loop is on theopposite side of said base member, each portion being connected to itsrespective remainder through said base member.

14. An antenna system comprising a base member of generally flatnon-electrically conductive material, a plurality of individualconductive loops distributed about said base member and connected inseries to form an overall loop, a plurality of individually adjustablecores arranged to move into and out of each loop and means forconnecting selected groups of loops to a receiving system.

15. An antenna system as in claim 14 wherein said individual loops areprovided with individually adjustable cores.

References Cited UNITED STATES PATENTS 2,451,291 10/1948 Koch 325-429 XR3,005,966 10/1961 StrOm 336-200 XR 3,119,065 1/1964 Blake 325-4283,151,297 9/1964 Toomin 325-429 3,185,947 5/1965 Freymodsson 3262003,296,535 l/l967 Murray 325-429 ROBERT L. GRIFFIN, Primary Examiner R.S. BELL, Assistant Examiner US. Cl. X.R.

